MOSCOW — A leading ally of Vladimir Putin said on Wednesday he was quitting his post as Russian parliament speaker, after polls that saw the ruling party lose support and face protests against vote-rigging.

Boris Gryzlov is the highest-profile casualty yet of the controversy surrounding the December 4 parliamentary elections that has for the first time shaken Putin’s decade-long domination of Russia.

“I have decided to renounce my mandate as a member of parliament… It would be wrong to occupy the post of speaker for more than two terms,” said Gryzlov in a statement on the website of the ruling United Russia party.

Gryzlov made no mention of the controversy surrounding the elections which saw United Russia win less than half the vote and then thousands take to the streets to accuse it of rigging the polls.

However he said he would continue in his post as chairman of United Russia, whose overall leader is Putin. Gryzlov had served two parliament terms as speaker since 2003.

Putin — who is preparing to move back to the presidency in 2012 polls from his current job as prime minister — is facing one of the biggest challenges to his 12-year rule of Russia amid the wave of protests.

The opposition have promised a new mass protest on December 24 in Moscow to follow a rally that drew tens of thousands at the weekend in the biggest show of public anger in Russia since the turbulent 1990s.

United Russia has come under attack by the opposition as a “party of swindlers and thieves”, a catchy slogan first made popular by the widely followed anti-corruption blogger Alexei Navalny.

Analysts have already predicted substantial shake-ups in the leadership of United Russia and the government as the authorities seek to respond to the party’s election performance ahead of the March 2012 presidential polls.

Gryzlov was mocked by the liberal press as a wooden speaker whose main interest was in keeping the State Duma as dull as possible.

He was once notoriously quoted as saying “the Duma is not a place for discussion” and one of his rituals was to wear a “lucky” woollen jumper on election nights.

Top United Russia official Andrei Vorobyev told the Interfax news agency that a new candidate for speaker could be agreed on Saturday.

The news agency said one of the favourites was Deputy Prime Minister Alexander Zhukov. The appointment of such a heavyweight figure would mark a significant rise in the profile of the job.

Yury Korgunyuk, an analyst at the INDEM foundation, said that with the opposition now far stronger in the new Duma, United Russia needed a stronger figure as speaker ahead of the first meeting of the new parliament on December 22.

“He is not a political fighter. He would be beaten. Previously it suited the authorities to have such a speaker. Now this is no longer the case,” he said.

With United Russia shaken by its failure to poll much more than 30 percent in some Russian regions, President Dmitry Medvedev accepted the resignation of the governor of the Vologda region Vyacheslav Pozgalyev.

United Russia only won 33.4% of the vote in the governor’s northern region and analysts expect more regional leaders to fall on their swords in the next months.

The elections have given Putin an uncomfortable three months leading up to the March presidential elections, which are expected to see Medvedev step aside and become prime minister.

Irkutsk region governor Dmitry Mezentsev on Wednesday announced his plan to run in the polls, although analysts doubted he even wanted to offer serious competition to Putin.

His entry was the latest surprise after billionaire Mikhail Prokhorov announced his candidacy in a dramatic announcement Tuesday.